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. 2019 Apr 19;9:6333. doi: 10.1038/s41598-019-42799-2

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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(a) Quinone redox cycling, ROS formation and GSH-based detoxification. A schematic of the single electron reduction of a quinone (Q) to a semiquinone radical anion (SQ^.−), followed by complete reduction to the hydroquinone (H₂Q). The figure shows the concomitant reduction of molecular oxygen by SQ^.− to form the ROS, superoxide (O₂^.−), followed by its dismutation into hydrogen peroxide (H₂O₂), which is detoxified by glutathione (GSH) into harmless H₂O through the glutathione peroxidase (GPx) reaction. GSH is regenerated from its oxidised form (GSSG), catalysed by the glutathione reduction (GR) reaction. Finally, the glutathione-quinone adduct (GS-H₂Q) formation represents the reductive addition (Michael reaction) between GSH and the Q electrophile. (b) Chemical structure of doxorubicin. The anthracycline contains both the quinone (red) and hydroquinone (blue) moieties within its chemical structure. The hydroquinone is the site of auto-oxidation for doxorubicin.